When the injector is electromagnetically operated, the injector needle valve is opened and closed by fuel pressure differential forces acting on both sides of an injector needle valve piston. An electromagnetically driven pilot valve controls the fuel pressure level on the back-side of the injector needle valve piston.
Different designs of fuel injectors of this type with an electromagnetic control of the injector needle valve are known and disclosed for example in the following publications: U.S. Pat. Nos. 2,881,980, 3,610,529 and 4,566,416 and European Published Patent Application No. 0 228 578. The injectors disclosed in the above mentioned publications are bulky, either because of the length of the injector and/or because of the particular design of the members responsible for the electromagnetic control of the injector needle valve. If these known injectors are used in small internal combustion engines, such as passenger car engines, this bulkiness is a considerable drawback. In addition, the above mentioned, relatively complex injector designs are expensive to manufacture. This is also playing a very important role in an application for small engines.
It is now a first object of the present invention to offer a very simple and compact design of the fuel injector with definite space-and price advantages compared to the prior art solutions. An injector design is simple if the number and the dimensions of the single components are small and if the number of tight fits and accurately machined surfaces are minimized. Furthermore the geometrical shape of the components must be so that the parts can be manufactured in a simple way. Finally it is an advantage if the finished components can be assembled and the complete injector can be calibrated by automated assembly and calibration machines.
It is a further object of the present invention to provide a fuel injector of very simple design which allows at the same time an improved control of the fuel injector performance compared to the prior art injectors. This is particularly the case when small amounts of fuel must be metered at a high fuel pressure during every intermittent injection event. This advantage, according to the present invention, is achieved by using a particular design of the electromagnets and electromagnetically driven pilot valves in conjunction with the hydraulically driven injector needle valve.
Those and further advantages of the invention become apparent from the following detailed description of various embodiments shown in the drawings.